The use of implantable vascular grafts comprised of PTFE are well known in the art. These types of grafts are typically used to replace or repair damaged or occluded blood vessels within the body. However, once such grafts are radially expanded within a blood vessel, they exhibit some retraction subsequent to expansion. Further, they require additional means for anchoring the graft within the blood vessel, such as sutures, clamps, or similarly functioning elements. In order to overcome the retraction disadvantage and eliminate the additional attachment means, those skilled in the art have used stents such as those presented by Palmaz in U.S. Pat. No. 4,733,665 and Gianturco in U.S. Pat. No. 4,580,568 which are herein incorporated by reference, either alone or in combination with PTFE grafts, in order to provide a non-retracting prosthesis having self-anchoring capability.
For example, the stent described by Palmaz in U.S. Pat. No. 4,733,665 is used to repair an occluded blood vessel by introducing the stent into the blood vessel via a balloon catheter, positioning the stent at the occluded site contained within the blood vessel, and expanding the stent to a diameter which is comparable to the diameter of the unoccluded blood vessel. The balloon catheter is then removed and the stent remains seated within the blood vessel due to the stent's ability to undergo radial expansion while limiting radial retraction. Further, use of radially expandable stents in combination with a PTFE graft is disclosed in U.S. Pat. No. 5,078,726 to Kreamer. Kreamer teaches placing a pair of expandable stents within the interior ends of a prosthetic graft having a length which is sufficient to span the weakened section of a blood vessel. The stents are then expanded to an increased diameter thereby securing the graft to the blood vessel wall via a friction fit.
However, although stents and stent/graft combinations have been used to provide endovascular prostheses which are capable of maintaining their fit against blood vessel walls, other desirable features are lacking. For instance, features such as increased strength and durability of the prosthesis, as well as an inert, smooth, biocompatible blood flow surface on the luminal surface of the prosthesis and an inert, smooth biocompatible surface on the abluminal surface of the prosthesis, are considered to be advantageous characteristics for an implantable vascular graft. Some of those skilled in the art have recently addressed these desirable characteristics by producing strengthened and reinforced prostheses composed entirely of biocompatible grafts and graft layers.
For example, U.S. Pat. No. 5,048,065, issued to Weldon, et al. discloses a reinforced graft assembly comprising a biologic or biosynthetic graft component having a porous surface and a biologic or biosynthetic reinforcing sleeve which is concentrically fitted over the graft component. The reinforcing sleeve includes an internal layer, an intermediate layer, and an external layer, all of which comprise biocompatible fibers. The sleeve component functions to provide compliant reinforcement to the graft component. Further, U.S. Pat. No. 5,163,951, issued to Pinchuk, et al. describes a composite vascular graft having an inner component, an intermediate component, and an outer component. The inner and outer components are preferably formed of expanded PTFE while the intermediate component is formed of strands of biocompatible synthetic material having a melting point less than the material which comprises the inner and outer components.
Another reinforced vascular prosthesis having enhanced compatibility and compliance is disclosed in U.S. Pat. No. 5,354,329, issued to Whalen. The Whalen patent describes a non-pyrogenic vascular prosthesis comprising a multilaminar tubular member having an interior strata, a unitary medial strata, and an exterior strata. The medial strata forms an exclusionary boundary between the interior and exterior strata. Also, one embodiment of the prosthesis is formed entirely of silicone rubber which comprises different characteristics for the different strata contained within the graft.
The prior art also includes grafts having increased strength and durability which have been reinforced with stent-like members. For example, U.S. Pat. No. 4,731,073, issued to Robinson discloses an arterial graft prosthesis comprising a multi-layer graft having a helical reinforcement embedded within the wall of the graft. U.S. Pat. No. 4,969,896, issued to Shors describes an inner elastomeric biocompatible tube having a plurality of rib members spaced about the exterior surface of the inner tube, and a perforate flexible biocompatible wrap circumferentially disposed about, and attached to, the rib members.
Another example of a graft having reinforcing stent-like members is disclosed in U.S. Pat. No. 5,123,917, issued to Lee. The Lee patent describes an expandable intraluminal vascular graft having an inner flexible cylindrical tube, an outer flexible cylindrical tube concentrically enclosing the inner tube, and a plurality of separate scaffold members positioned between the inner and outer tubes. Further, U.S. Pat. No. 5,282,860, issued to Matsuno, et al. discloses a multi-layer stent comprising an outer resin tube having at least one flap to provide an anchoring means, an inner fluorine-based resin tube and a mechanical reinforcing layer positioned between the inner and outer tubes.
Another stent containing graft is described in U.S. Pat. No. 5,389,106 issued to Tower. The Tower patent discloses an impermeable expandable intravascular stent which includes a distensible frame and an impermeable deformable membrane interconnecting portions of the frame to form an impermeable exterior wall. The membrane comprises a synthetic non-latex, non-vinyl polymer while the frame is comprised of a fine platinum wire. The membrane is attached to the frame by placing the frame on a mandrel, dipping the frame and the mandrel into a polymer and organic solvent solution, withdrawing the frame and mandrel from the solution, drying the frame and mandrel, and removing the mandrel from the frame.
Although the previously described reinforced grafts disclose structures which have increased strength and durability, as well as inert, smooth inner and outer surfaces to reduce thrombogenicity, the prior art references do not disclose a device which exhibits these advantageous characteristics in addition to good resistance to radial contraction and possible self anchoring means. Accordingly, there is a need for a radially expandable reinforced vascular graft having good resistance to radial contraction and means for self anchoring which also exhibits increased strength, increased durability, and inertness with respect to its interior and exterior surfaces.